IMAP and POP3 Clients in C#

using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace LumiSoft.Net.UDP
{
    /// <summary>
    /// This class implements generic UDP server.
    /// </summary>
    public class UDP_Server : IDisposable
    {      
        private bool                     m_IsDisposed         = false;
        private bool                     m_IsRunning          = false;
        private int                      m_MTU                = 1400;
        private IPEndPoint[]             m_pBindings          = null;
        private DateTime                 m_StartTime;
        private List<Socket>             m_pSockets           = null;
        private CircleCollection<Socket> m_pSendSocketsIPv4   = null;
        private CircleCollection<Socket> m_pSendSocketsIPv6   = null;
        private int                      m_ReceiversPerSocket = 10;
        private List<UDP_DataReceiver>   m_pDataReceivers     = null;
        private long                     m_BytesReceived      = 0;
        private long                     m_PacketsReceived    = 0;
        private long                     m_BytesSent          = 0;
        private long                     m_PacketsSent        = 0;

        /// <summary>
        /// Default constructor.
        /// </summary>
        public UDP_Server()
        {        
        }

        #region method Dispose

        /// <summary>
        /// Cleans up any resources being used.
        /// </summary>
        public void Dispose()
        {
            if(m_IsDisposed){
                return;
            }
            m_IsDisposed = false;
            Stop();
            // Release all events.
            this.Error = null;
            this.PacketReceived = null;
        }

        #endregion


        #region method Start

        /// <summary>
        /// Starts UDP server.
        /// </summary>
        public void Start()
        {
            if(m_IsRunning){
                return;
            }
            m_IsRunning = true;

            m_StartTime = DateTime.Now;
            m_pDataReceivers = new List<UDP_DataReceiver>();

            // Run only if we have some listening point.
            if(m_pBindings != null){
                // We must replace IPAddress.Any to all available IPs, otherwise it's impossible to send 
                // reply back to UDP packet sender on same local EP where packet received. This is very 
                // important when clients are behind NAT.
                List<IPEndPoint> listeningEPs = new List<IPEndPoint>();
                foreach(IPEndPoint ep in m_pBindings){                    
                    if(ep.Address.Equals(IPAddress.Any)){
                        // Add localhost.
                        IPEndPoint epLocalhost = new IPEndPoint(IPAddress.Loopback,ep.Port);
                        if(!listeningEPs.Contains(epLocalhost)){
                            listeningEPs.Add(epLocalhost);
                        }
                        // Add all host IPs.
                        foreach(IPAddress ip in System.Net.Dns.GetHostAddresses("")){
                            IPEndPoint epNew = new IPEndPoint(ip,ep.Port);
                            if(!listeningEPs.Contains(epNew)){
                                listeningEPs.Add(epNew);
                            }
                        }
                    }
                    else{
                        if(!listeningEPs.Contains(ep)){
                            listeningEPs.Add(ep);
                        }
                    }
                }

                // Create sockets.
                m_pSockets = new List<Socket>();
                foreach(IPEndPoint ep in listeningEPs){                    
                    try{
                        Socket socket = Net_Utils.CreateSocket(ep,ProtocolType.Udp);
                        m_pSockets.Add(socket);

                        // Create UDP data receivers.
                        for(int i=0;i<m_ReceiversPerSocket;i++){
                            UDP_DataReceiver receiver = new UDP_DataReceiver(socket);
                            receiver.PacketReceived += delegate(object s,UDP_e_PacketReceived e){
                                try{
                                    ProcessUdpPacket(e);
                                }
                                catch(Exception x){
                                    OnError(x);
                                }
                            };
                            receiver.Error += delegate(object s,ExceptionEventArgs e){
                                OnError(e.Exception);
                            };
                            m_pDataReceivers.Add(receiver);
                            receiver.Start();
                        }
                    }
                    catch(Exception x){
                        OnError(x);
                    }
                }
           
                // Create round-robin send sockets. NOTE: We must skip localhost, it can't be used 
                // for sending out of server.
                m_pSendSocketsIPv4 = new CircleCollection<Socket>();
                m_pSendSocketsIPv6 = new CircleCollection<Socket>();
                foreach(Socket socket in m_pSockets){
                    if(((IPEndPoint)socket.LocalEndPoint).AddressFamily == AddressFamily.InterNetwork){
                        if(!((IPEndPoint)socket.LocalEndPoint).Address.Equals(IPAddress.Loopback)){                            
                            m_pSendSocketsIPv4.Add(socket);
                        }
                    }
                    else if(((IPEndPoint)socket.LocalEndPoint).AddressFamily == AddressFamily.InterNetworkV6){
                        m_pSendSocketsIPv6.Add(socket);
                    }                    
                }
            }
        }

        #endregion

        #region method Stop

        /// <summary>
        /// Stops UDP server.
        /// </summary>
        public void Stop()
        {
            if(!m_IsRunning){
                return;
            }
            m_IsRunning = false;

            foreach(UDP_DataReceiver receiver in m_pDataReceivers){
                receiver.Dispose();
            }
            m_pDataReceivers = null; 
            foreach(Socket socket in m_pSockets){
                socket.Close();
            }
            m_pSockets = null;
            m_pSendSocketsIPv4 = null;
            m_pSendSocketsIPv6 = null;
        }

        #endregion

        #region method Restart

        /// <summary>
        /// Restarts running server. If server is not running, this methods has no efffect.
        /// </summary>
        public void Restart()
        {
            if(m_IsRunning){
                Stop();
                Start();
            }
        }

        #endregion


        #region method SendPacket
                
        /// <summary>
        /// Sends specified UDP packet to the specified remote end point.
        /// </summary>
        /// <param name="packet">UDP packet to send.</param>
        /// <param name="offset">Offset in the buffer.</param>
        /// <param name="count">Number of bytes to send.</param>
        /// <param name="remoteEP">Remote end point.</param>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this method is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this method is accessed.</exception>
        /// <exception cref="ArgumentNullException">Is raised when any of the arumnets is null.</exception>
        /// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
        public void SendPacket(byte[] packet,int offset,int count,IPEndPoint remoteEP)
        {
            IPEndPoint localEP = null;
            SendPacket(packet,offset,count,remoteEP,out localEP);
        }

        /// <summary>
        /// Sends specified UDP packet to the specified remote end point.
        /// </summary>
        /// <param name="packet">UDP packet to send.</param>
        /// <param name="offset">Offset in the buffer.</param>
        /// <param name="count">Number of bytes to send.</param>
        /// <param name="remoteEP">Remote end point.</param>
        /// <param name="localEP">Returns local IP end point which was used to send UDP packet.</param>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this method is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this method is accessed.</exception>
        /// <exception cref="ArgumentNullException">Is raised when any of the arumnets is null.</exception>
        /// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
        public void SendPacket(byte[] packet,int offset,int count,IPEndPoint remoteEP,out IPEndPoint localEP)
        {
            if(m_IsDisposed){
                throw new ObjectDisposedException("UdpServer");
            }
            if(!m_IsRunning){
                throw new InvalidOperationException("UDP server is not running.");
            }
            if(packet == null){
                throw new ArgumentNullException("packet");
            }
            if(remoteEP == null){
                throw new ArgumentNullException("remoteEP");
            }

            localEP = null;
            SendPacket(null,packet,offset,count,remoteEP,out localEP);
        }

        /// <summary>
        /// Sends specified UDP packet to the specified remote end point.
        /// </summary>
        /// <param name="localEP">Local end point to use for sending.</param>
        /// <param name="packet">UDP packet to send.</param>
        /// <param name="offset">Offset in the buffer.</param>
        /// <param name="count">Number of bytes to send.</param>
        /// <param name="remoteEP">Remote end point.</param>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this method is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this method is accessed.</exception>
        /// <exception cref="ArgumentNullException">Is raised when any of the arumnets is null.</exception>
        /// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
        public void SendPacket(IPEndPoint localEP,byte[] packet,int offset,int count,IPEndPoint remoteEP)
        {
            if(m_IsDisposed){
                throw new ObjectDisposedException("UdpServer");
            }
            if(!m_IsRunning){
                throw new InvalidOperationException("UDP server is not running.");
            }
            if(packet == null){
                throw new ArgumentNullException("packet");
            }
            if(localEP == null){
                throw new ArgumentNullException("localEP");
            }        
            if(remoteEP == null){
                throw new ArgumentNullException("remoteEP");
            }
            if(localEP.AddressFamily != remoteEP.AddressFamily){
                throw new ArgumentException("Argumnet localEP and remoteEP AddressFamily won't match.");
            }

            // Search specified local end point socket.
            Socket socket = null;
            if(localEP.AddressFamily == AddressFamily.InterNetwork){
                foreach(Socket s in m_pSendSocketsIPv4.ToArray()){
                    if(localEP.Equals((IPEndPoint)s.LocalEndPoint)){
                        socket = s;
                        break;
                    }
                }
            }
            else if(localEP.AddressFamily == AddressFamily.InterNetworkV6){
                foreach(Socket s in m_pSendSocketsIPv6.ToArray()){
                    if(localEP.Equals((IPEndPoint)s.LocalEndPoint)){
                        socket = s;
                        break;
                    }
                }
            }
            else{
                throw new ArgumentException("Argument 'localEP' has unknown AddressFamily.");
            }

            // We don't have specified local end point.
            if(socket == null){
                throw new ArgumentException("Specified local end point '" + localEP + "' doesn't exist.");
            }
                        
            IPEndPoint lEP = null;
            SendPacket(socket,packet,offset,count,remoteEP,out lEP);
        }

        /// <summary>
        /// Sends specified UDP packet to the specified remote end point.
        /// </summary>
        /// <param name="socket">UDP socket to use for data sending.</param>
        /// <param name="packet">UDP packet to send.</param>
        /// <param name="offset">Offset in the buffer.</param>
        /// <param name="count">Number of bytes to send.</param>
        /// <param name="remoteEP">Remote end point.</param>
        /// <param name="localEP">Returns local IP end point which was used to send UDP packet.</param>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this method is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this method is accessed.</exception>
        /// <exception cref="ArgumentNullException">Is raised when any of the arumnets is null.</exception>
        /// <exception cref="ArgumentException">Is raised when any of the arguments has invalid value.</exception>
        internal void SendPacket(Socket socket,byte[] packet,int offset,int count,IPEndPoint remoteEP,out IPEndPoint localEP)
        {
            // Round-Robin all local end points, if no end point specified.
            if(socket == null){
                // Get right IP address family socket which matches remote end point.
                if(remoteEP.AddressFamily == AddressFamily.InterNetwork){
                    if(m_pSendSocketsIPv4.Count == 0){
                        throw new ArgumentException("There is no suitable IPv4 local end point in this.Bindings.");
                    }

                    socket = m_pSendSocketsIPv4.Next();
                }
                else if(remoteEP.AddressFamily == AddressFamily.InterNetworkV6){
                    if(m_pSendSocketsIPv6.Count == 0){
                        throw new ArgumentException("There is no suitable IPv6 local end point in this.Bindings.");
                    }

                    socket = m_pSendSocketsIPv6.Next();
                }
                else{
                    throw new ArgumentException("Invalid remote end point address family.");
                }
            }

            // Send packet.
            socket.SendTo(packet,0,count,SocketFlags.None,remoteEP);

            localEP = (IPEndPoint)socket.LocalEndPoint;

            m_BytesSent += count;
            m_PacketsSent++;
        }

        #endregion

        #region method GetLocalEndPoint

        /// <summary>
        /// Gets suitable local IP end point for the specified remote endpoint.
        /// If there are multiple sending local end points, they will be load-balanched with round-robin.
        /// </summary>
        /// <param name="remoteEP">Remote end point.</param>
        /// <returns>Returns local IP end point.</returns>
        /// <exception cref="ArgumentNullException">Is raised when argument <b>remoteEP</b> is null.</exception>
        /// <exception cref="ArgumentException">Is raised when argument <b>remoteEP</b> has invalid value.</exception>
        /// <exception cref="InvalidOperationException">Is raised when no suitable IPv4 or IPv6 socket for <b>remoteEP</b>.</exception>
        public IPEndPoint GetLocalEndPoint(IPEndPoint remoteEP)
        {
            if(remoteEP == null){
                throw new ArgumentNullException("remoteEP");
            }

            if(remoteEP.AddressFamily == AddressFamily.InterNetwork){
                // We don't have any IPv4 local end point.
                if(m_pSendSocketsIPv4.Count == 0){
                    throw new InvalidOperationException("There is no suitable IPv4 local end point in this.Bindings.");
                }

                return (IPEndPoint)m_pSendSocketsIPv4.Next().LocalEndPoint;
            }
            else if(remoteEP.AddressFamily == AddressFamily.InterNetworkV6){
                // We don't have any IPv6 local end point.
                if(m_pSendSocketsIPv6.Count == 0){
                    throw new InvalidOperationException("There is no suitable IPv6 local end point in this.Bindings.");
                }

                return (IPEndPoint)m_pSendSocketsIPv6.Next().LocalEndPoint;
            }
            else{
                throw new ArgumentException("Argument 'remoteEP' has unknown AddressFamily.");
            }
        }

        #endregion


        #region method ProcessUdpPacket

        /// <summary>
        /// Processes specified incoming UDP packet.
        /// </summary>
        /// <param name="e">Packet event data.</param>
        /// <exception cref="ArgumentNullException">Is raised when <b>e</b> is null reference.</exception>
        private void ProcessUdpPacket(UDP_e_PacketReceived e)
        {
            if(e == null){
                throw new ArgumentNullException("e");
            }

            OnUdpPacketReceived(e);
        }

        #endregion


        #region Properties Implementation

        /// <summary>
        /// Gets if this object is disposed.
        /// </summary>
        public bool IsDisposed
        {
            get{ return m_IsDisposed; }
        }

        /// <summary>
        /// Gets if UDP server is running.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        public bool IsRunning
        {
            get{ 
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }

                return m_IsRunning;
            }
        }

        /// <summary>
        /// Gets or sets maximum network transmission unit.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised when server is running and this property value is tried to set.</exception>
        public int MTU
        {
            get{ 
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }

                return m_MTU; 
            }

            set{
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(m_IsRunning){
                    throw new InvalidOperationException("MTU value can be changed only if UDP server is not running.");
                }

                m_MTU = value;
            }
        }

        /// <summary>
        /// Gets or sets IP end point where UDP server is binded.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="ArgumentNullException">Is raised when null value is passed.</exception>
        public IPEndPoint[] Bindings
        {
            get{ 
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }

                return m_pBindings; 
            }

            set{
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(value == null){
                    throw new ArgumentNullException();
                }

                // See if changed. Also if server running we must restart it.
                bool changed = false;
                if(m_pBindings == null){
                    changed = true;
                }
                else if(m_pBindings.Length != value.Length){
                    changed = true;
                }
                else{
                    for(int i=0;i<m_pBindings.Length;i++){
                        if(!m_pBindings[i].Equals(value[i])){
                            changed = true;
                            break;
                        }
                    }
                }               
                if(changed){
                    m_pBindings = value;
                    Restart();
                }
            }
        }

        /// <summary>
        /// Gets time when server was started.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this property is accessed.</exception>
        public DateTime StartTime
        {
            get{ 
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(!m_IsRunning){
                    throw new InvalidOperationException("UDP server is not running.");
                }

                return m_StartTime; 
            }
        }

        /// <summary>
        /// Gets how many bytes this UDP server has received since start.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this property is accessed.</exception>
        public long BytesReceived
        {
            get{               
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(!m_IsRunning){
                    throw new InvalidOperationException("UDP server is not running.");
                }

                return m_BytesReceived; 
            }
        }

        /// <summary>
        /// Gets how many UDP packets this UDP server has received since start.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this property is accessed.</exception>
        public long PacketsReceived
        {
            get{               
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(!m_IsRunning){
                    throw new InvalidOperationException("UDP server is not running.");
                }

                return m_PacketsReceived; 
            }
        }

        /// <summary>
        /// Gets how many bytes this UDP server has sent since start.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this property is accessed.</exception>
        public long BytesSent
        {
            get{               
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(!m_IsRunning){
                    throw new InvalidOperationException("UDP server is not running.");
                }

                return m_BytesSent; 
            }
        }

        /// <summary>
        /// Gets how many UDP packets this UDP server has sent since start.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this property is accessed.</exception>
        /// <exception cref="InvalidOperationException">Is raised whan UDP server is not running and this property is accessed.</exception>
        public long PacketsSent
        {
            get{               
                if(m_IsDisposed){
                    throw new ObjectDisposedException("UdpServer");
                }
                if(!m_IsRunning){
                    throw new InvalidOperationException("UDP server is not running.");
                }

                return m_PacketsSent; 
            }
        }

        #endregion

        #region Events Implementation

        /// <summary>
        /// This event is raised when new UDP packet received.
        /// </summary>
        public event EventHandler<UDP_e_PacketReceived> PacketReceived = null;

        #region method OnUdpPacketReceived

        /// <summary>
        /// Raises PacketReceived event.
        /// </summary>
        /// <param name="e">Event data.</param>
        private void OnUdpPacketReceived(UDP_e_PacketReceived e)
        {            
            if(this.PacketReceived != null){
                this.PacketReceived(this,e);
            }
        }

        #endregion

        /// <summary>
        /// This event is raised when unexpected error happens.
        /// </summary>
        public event ErrorEventHandler Error = null;

        #region method OnError

        /// <summary>
        /// Raises Error event.
        /// </summary>
        /// <param name="x">Exception occured.</param>
        private void OnError(Exception x)
        {
            if(this.Error != null){
                this.Error(this,new Error_EventArgs(x,new System.Diagnostics.StackTrace()));
            }
        }

        #endregion

        #endregion

    }
}